Iron-Catalyzed Cross-Coupling of Unactivated Secondary Alkyl Thio Ethers and Sulfones with Aryl Grignard Reagents
作者:Scott E. Denmark、Alexander J. Cresswell
DOI:10.1021/jo402246h
日期:2013.12.20
ed cross-coupling are described. Initial studies focused on discerning the structural and electronic features of the organosulfur substrate that enable the challenging oxidative addition to the C(sp3)–S bond. Through extensive optimization efforts, an Fe(acac)3-catalyzed cross-coupling of unactivated alkyl aryl thio ethers with aryl Grignardreagents was realized in which a nitrogen “directing group”
Experimental Evidence for Negative Hyperconjugation as a Component of the Polar Effect: Variation of the Ease of α-Sulfonyl Carbanion Formation with the Orientation of a β-Alkoxy Substituent
作者:James F. King、Rajendra Rathore、Zhenrong Guo、Manqing Li、Nicholas C. Payne
DOI:10.1021/ja001320l
日期:2000.10.1
the incipient carbanion into the # C-O / orbital. This effect is largest with torsion angles of 0 and 180ϒ and at these torsion angles constitutes the major source of stabilization of the incipient carbanion by the ! -alkoxy group. The present observation of a torsion-angle-dependent substituent effect may be combined with the known adherence of the specific rate of R-sulfonyl carbanion formation to
我们报告了强烈依赖几何的取代基效应的证据。R-氢的 HD 交换速率常数 (kexch)OR,在一组 19 ! - 已知的、固定的(或强烈优选的)H-CR-C 的烷氧基砜!- 或已测量扭转角。还测量了缺少烷氧基的相应模型化合物 (kexch) 模型的那些,从而提供比率 kN ) (kexch)OR/(kexch) 模型;如此获得的 kN 值范围超过 4 个数量级。我们表明,当考虑到空间和其他影响时,我们的观察结果与 log kN ) a + b cos 2 " (其中 a ) 1.70 ( 0.17 和 b ) 2.62 ( 0.20) 形式的方程一致。它是进一步表明,观察到的速率常数比与仅由感应效应和场效应组成的取代效应不一致,并且它们与第三种效应的额外存在完全一致,即负超共轭或广义异头效应,特别是初始碳负离子的部分负电荷向#CO/轨道的扭转角依赖性捐赠。这种效应在扭转角为 0 和 180